1. Field of the Invention
The invention is in the field of conveying technology. It pertains to a clamping element for fitting onto a clamping tongue of a gripper as well as a gripper with this kind of clamping element.
2. Description of Related Art
The publication WO 2007/115421 describes a gripper comprising two clamping tongues as well as a means for generating a clamping force. The clamping tongues are pivotable in relation to one another on a pivot axis between two extreme positions, which corresponds to an open or closed configuration of the gripper respectively. At least one of the clamping tongues comprises, on its outer edge, two laterally protruding springing arms, i.e. protruding in parallel to the pivot axis. On these arms per clamping tongue two clamping elements are attached, in order to divide the clamping force between the two points or regions respectively and to make it uniform within these clamping regions.
Clamping elements, which, as described in WO 2007/115421, are attached only by attaching them on the clamping tongues, have the disadvantage that they may come off the clamping tongues during operation, in particular in that the small displacements occurring during operation add up, such that the clamping element falls off the arm laterally.
A rubber coating fixed permanently to the clamping tongue is already known from DE-A 310 22 42. The rubber coating is on the one hand to protect the product from being damaged and on the other hand to increase the adhesion between the clamping tongues and the product. The clamping tongue is, however, compared to the objects to be gripped, relatively narrow. On the other hand the clamping force is exerted over an extended region. With objects with variations in thickness, e.g. due to inserted products this may lead to the clamping force being concentrated to one single point, namely the location of the greatest thickness, and the held objects may twist around this point.
The invention, thus, has the object to provide a clamping element for grippers, which in case of wear may be easily exchanged, in mounted condition, however, is reliably fixed to the clamping tongue of the gripper and is, thus, suitable for continuous duty. Apart from this it is a further object of the invention to guarantee a reliable clamping effect and a stable product position.
The clamping element according to the invention is adapted to grippers on which at least one clamping tongue is formed in a T-shape, i.e. comprises two arms laterally protruding from a central clamping tongue part. For removable fastening of the clamping element to the clamping tongue at least one fastening element, preferably two fastening elements are provided. With the fastening element(s), the clamping element may be fitted to the clamping tongue in a planar manner or in several fastening locations respectively. According to the invention, the clamping element has a lengthy carrier, the width of which substantially corresponds to the width of the clamping tongue in the region of the arms, which thus can cover the arms over their complete width. For secure holding of an object, at least two distanced clamping regions are provided, which are arranged on the carrier such that they are located in the region of the arms in the case of use. The clamping regions may be designed in one piece with the carrier or they may be elements connected to the carrier, which define the clamping regions.
The invention thus suggests using, instead of several clamping elements fitted to the clamping tongue unilaterally, an extended carrier, on which at least two clamping regions are realised and which may be fastened to the arms of the clamping tongue in a suitable manner.
The term clamping region means the region of the clamping elements in which in the case of application the clamping forces are mainly transmitted to the held object. By means of the two or more independent clamping regions, a clamping effect concentrated to different regions is realised. A dislocation of the product is thus impeded even if it comprises variations in thickness in the held regions. This can be supported by fitting the arms on the central clamping tongue part in a springing manner, which thus may additionally compensate thickness variations. The clamping regions differ from the rest of the regions of the carrier, e.g. by having an enlarged cross section (e.g. cushion-type swelling in the carrier) and/or by means of the elasticity module, in particular lower compliance in clamping direction. In the clamping region, preferably a certain elasticity/flexibility is provided in order to make the clamped force constant over the clamped area by means of adaptation to the form of the counter element or to the product and in particular to achieve a frontal area running in parallel to the product or the counter element respectively.
By realising two or more clamping areas on the same carrier, these being allocated to the two arms arranged in symmetry to one another, forces can additionally be made constant, which act on the clamping element during operation and e.g. in the case of a carrier and clamping region allocated to only one arm, may lead to a detachment of the carrier.
The manner of the fastening on the clamping tongue is preferably adapted to the form of the clamping tongue, in particular the fastening elements act together with the clamping tongue by means of form or force engagement, e.g. by enclosing these or the two arms respectively between them. The fastening elements preferably limit the region in which the clamping element may be displaced in relation to the clamping tongue, such that no unintended detachment of the clamping element can occur. The fastening element is e.g. extended in a planar manner and reaches over the whole width of the clamping tongue. Alternatively, at least two mutually distanced fastening elements may be provided.
The fastening elements may e.g. be brackets with which the carrier is fitted to the clamping tongue and which reach over the complete width of the carrier or which may be arranged on the faces of the carrier. Fastening elements such as bolts or the like or a latching connection are also possible. In a preferred embodiment, the carrier itself is flexible at least in regions and may be deformed such that it can be applied onto the clamping tongue under the effect of force and in unstressed condition is held on it, in particular by form or force engagement.
The gripper according to the invention has, as known per se, a first and a second clamping tongue as well as a means for generating a clamping force, e.g. a spring. The clamping tongues each comprise on their distal ends clamping elements and are pivotable on a pivot axis in relation to each other such that the gripper may be brought into an open configuration or a closed configuration respectively, wherein the clamping elements of both clamping tongues lie upon each other or on the flat object in the closed configuration and are pressed against each other by the clamping force. At least one of the clamping tongues comprises two lateral arms, such that a T-shape is formed. At least one of the clamping elements is, as described above, designed with a lengthy carrier, at least two clamping regions and at least one fastening element and detachably fastened to the T-shaped clamping tongue.
Preferably, the clamping element substantially extends over the complete width of the clamping tongue including the arms and is preferably detachably fastened on both arms.
The invention has the advantage that the clamping elements, by means of the division of force onto two clamping regions enable a reliable holding of the objects by the gripper. They are easily exchangeable when worn or contaminated, however, are not displaced during operation or only to a low degree in relation to the clamping tongue.